The subject matter disclosed herein relates to refrigeration systems. More specifically, the subject matter disclosed herein relates to refrigeration of containers utilized to store and ship cargo.
A typical refrigerated cargo container or refrigerated truck trailer, such as those utilized to transport a cargo via sea, rail or road, is a container modified to include a refrigeration unit located at one end of the container. The refrigeration unit includes a compressor, condenser, expansion valve and evaporator serially connected by refrigerant lines in a closed refrigerant circuit in accord with known refrigerant vapor compression cycles. A power unit, including an engine, drives the compressor of the refrigeration unit, and is typically diesel powered, or in other applications natural gas powered. In many truck/trailer transport refrigeration systems, the compressor is driven by the engine shaft either through a belt drive or by a mechanical shaft-to-shaft link. In other systems, the engine drives a generator that generates electrical power, which in turn drives the compressor.
As stated above, diesel fuel is typically utilized to power the engine. Alternatives such as compressed natural gas (CNG) and liquid natural gas (LNG) are used as engine fuel sources in some systems. CNG-fueled systems have difficulties, however, with containment of the high-pressure CNG, as well as the relatively low energy output of the CNG fuel. LNG is often more cost effective than diesel, but the LNG must be heated to gasify, or regenerate, the LNG into gaseous methane prior to introduction of the fuel into the engine. This regeneration is typically achieved by use of an electric heater in the fuel system, or by utilizing waste heat from the engine to gasify the methane LNG.